sysvinit-2.86/src/mesg.c

   1 /*
   2  * mesg.c       The "mesg" utility. Gives / restrict access to
   3  *              your terminal by others.
   4  *
   5  * Usage:       mesg [y|n].
   6  *              Without arguments prints out the current settings.
   7  *
   8  *              This file is part of the sysvinit suite,
   9  *              Copyright 1991-2001 Miquel van Smoorenburg.
  10  *
  11  *              This program is free software; you can redistribute it and/or
  12  *              modify it under the terms of the GNU General Public License
  13  *              as published by the Free Software Foundation; either version
  14  *              2 of the License, or (at your option) any later version.
  15  */
  16 #include <sys/types.h>
  17 #include <sys/stat.h>
  18 #include <stdio.h>
  19 #include <stdlib.h>
  20 #include <string.h>
  21 #include <errno.h>
  22 #include <unistd.h>
  23 #include <grp.h>
  24
  25 char *Version = "@(#) mesg 2.81 31-Jul-2001 miquels@cistron.nl";
  26
  27 #define TTYGRP          "tty"
  28
  29 /*
  30  *      See if the system has a special 'tty' group.
  31  *      If it does, and the tty device is in that group,
  32  *      we set the modes to -rw--w--- instead if -rw--w--w.
  33  */
  34 int hasttygrp(void)
  35 {
  36         struct group *grp;
  37
  38         if ((grp = getgrnam(TTYGRP)) != NULL)
  39                 return 1;
  40         return 0;
  41 }
  42
  43
  44 /*
  45  *      See if the tty devices group is indeed 'tty'
  46  */
  47 int tty_in_ttygrp(struct stat *st)
  48 {
  49         struct group *gr;
  50
  51         if ((gr = getgrgid(st->st_gid)) == NULL)
  52                 return 0;
  53         if (strcmp(gr->gr_name, TTYGRP) != 0)
  54                 return 0;
  55
  56         return 1;
  57 }
  58
  59 int main(int argc, char **argv)
  60 {
  61         struct stat     st;
  62         unsigned int    ttymode, st_mode_old;
  63         int             ht;
  64         int             it;
  65         int             e;
  66
  67         if (!isatty(0)) {
  68                 /* Or should we look in /var/run/utmp? */
  69                 fprintf(stderr, "stdin: is not a tty\n");
  70                 return(1);
  71         }
  72
  73         if (fstat(0, &st) < 0) {
  74                 perror("fstat");
  75                 return(1);
  76         }
  77
  78         ht = hasttygrp();
  79         it = tty_in_ttygrp(&st);
  80
  81         if (argc < 2) {
  82                 ttymode = (ht && it) ? 020 : 002;
  83                 printf("is %s\n", (st.st_mode & ttymode) ? "y" : "n");
  84                 return 0;
  85         }
  86         if (argc > 2 || (argv[1][0] != 'y' && argv[1][0] != 'n')) {
  87                 fprintf(stderr, "Usage: mesg [y|n]\n");
  88                 return 1;
  89         }
  90
  91         /*
  92          *      Security check: allow mesg n when group is
  93          *      weird, but don't allow mesg y.
  94          */
  95         ttymode = ht ? 020 : 022;
  96         if (ht && !it && argv[1][0] == 'y') {
  97                 fprintf(stderr, "mesg: error: tty device is not owned "
  98                         "by group `%s'\n", TTYGRP);
  99                 exit(1);
 100         }
 101
 102         st_mode_old = st.st_mode;
 103         if (argv[1][0] == 'y')
 104                 st.st_mode |= ttymode;
 105         else
 106                 st.st_mode &= ~(ttymode);
 107         if (st_mode_old != st.st_mode && fchmod(0, st.st_mode) != 0) {
 108                 e = errno;
 109                 fprintf(stderr, "mesg: %s: %s\n",
 110                         ttyname(0), strerror(e));
 111                 exit(1);
 112         }
 113
 114         return 0;
 115 }